1. Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
2. Icelandic Heart Association, Reykjavik, Iceland
3. Intramural Research Program, National Institute on Aging, National Institutes of Health, Bethesda, MD
4. Cardiovascular and Pulmonary Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD